ok I am a benevolent god ;P so I will help you guys out.
I bought 2 xfx 290x's for $340 each. Shipping was $80(insured, don't rely on ebay buyer protection I have had them randomly close cases on me and say there is nothing they can do to reopen it even if it is an ebay error) each, customs was R600 each
So around R4800 each, Shippied via usps priority it took 20 days to arrive. My cards are currently untested as my motherboard is on an rma so I will update once it is back but both cards look perfect.
xfx will honor the warranty, I have had it once that they paid shipping from SA to the US but don't count on it. IF you need to ship it back it till cost R800 each way if you are lucky but yeah it is worth it because they replace their cards with new ones.
DO NOT BUY FROM CANADA, shipping is $100 at least. IT takes longer too, the canada postal service is bankrupt so yeah...
You can get it for cheaper, I saw a guy list 5 290x's and the lowest one went for $201 and I am damn sad I did not bid on it. You will also see some listings where the seller ships internationally that ebay works out customs fees etc for you but they are rarer and go for more money. You will need to ask each seller politely if he will ship to south africa and what will it cost to ship via flat rate usps priority.
Other brands you will have to contact each brand to find out what they do in regards to warranty. Some are serial based but you need to live in the country of origin to rma and all that jazz.